java - Double.Min_Value 未按预期工作

Question

我有以下代码，但当 mutuaInformation 为零时它不会通过 if。知道出了什么问题吗？

        int largestEntropyIndex = Integer.MIN_VALUE;
        double largestMutualInfomation = Double.MIN_VALUE;
        for (int i = 0; i < attributes.size(); i++) {
            String attrName=this.attributes.get(i);
            double conditionalEntropy = calcConditionalEntropy(i,
                                                               instances,
                                                               this.attributeValues.get(attrName).size(),
                                                               this.labels.size());

            System.out.println("conditional entropy is: "+conditionalEntropy);
            double mutualInformation = entropy - conditionalEntropy;
            if (mutualInformation > largestMutualInfomation){
                largestMutualInfomation = mutualInformation;
                largestEntropyIndex = i;
            }

Answer 1

Double.MIN_VALUE持有正数，所以 0 < Double.MIN_VALUE .

/**
 * A constant holding the smallest positive nonzero value of type
 * <code>double</code>, 2<sup>-1074</sup>. It is equal to the
 * hexadecimal floating-point literal
 * <code>0x0.0000000000001P-1022</code> and also equal to
 * <code>Double.longBitsToDouble(0x1L)</code>.
 */
public static final double MIN_VALUE = 0x0.0000000000001P-1022; // 4.9e-324

您应该改用一些任意的负值(或者可能是 Double.NEGATIVE_INFINITY )。